A standard single-control mixing valve has a housing in which is provided a ceramic-plate valve cartridge in turn having an actuating element that can be pivoted about a normally horizontal element axis to control flow volume through the valve and that can also be pivoted about a normally vertical axis to control the temperature of the water flowing out of a faucet fed by the valve. An actuating shaft fixed to the actuating element is coupled at each of its ends to a lever that is shaped like a two-tine fork with a pair of end pins each connected to a respective end of the actuating shaft.
As described in German patent document 3,427,95 filed on 28 July 1984 by Helmut Zwink and Hans Oberdorfer the actuating shaft projects at both ends beyond the sleeve and cap that cover the valve housing and enclose the cartridge. These shaft ends are each of square shape and fit into complementary seats in the end pins of the actuating fork.
In order to accommodate some difference in the length of the shaft from valve model to model as well as in the spacing between the end pins of the actuating fork it is standard to leave some play in the fit between the end pins and the actuating shaft. This play must be provided at some remove from where the actuating shaft is seated in the cartridge actuating element, so that with use the play increases, getting so loose and sloppy that with time the end pins can fall right off the shaft ends. The holes where the shaft end project through the casing formed by the sleeve and cap are also fairly loose to compensate for poor manufacturing tolerances and therefore are also sites where water can get into the valve.